680  PRE-CAMBRIAN    GEOLOGY   OF    NORTH   AMERICA. 
is  the  axis  of  the  State  and  is  composed  for  the  most  part  of  granitic 
and  gneissic  rocks  which  are  extremely  metamorphosed.  These 
rocks,  as  well  as  the  slates  and  schists,  belong  to  the  most  ancient  of 
the  Azoic  series,  and  the  Black  Mountains  are  the  oldest  part  of  this 
Azoic. 
Kerr,68  in  1875,  gives  a  systematic  account  of  the  geology  of  North 
Carolina.  The  Azoic  rocks  are  divided  into  Hnronian,  Lanrentian, 
and  igneous.  With  the  Huronian  are  placed  the  siliceous  and  argil- 
laceous slates  and  conglomerates,  micaceous  and  hornblendic  slates  and 
schists,  chlorites,  quartzites,  and  diorites,  with  cherty,  jaspery,  and 
epidotic  beds,  and  much  specular  iron  ore.  The  Laurentian  includes 
gneiss,  granite,  hornblende  slates,  etc.,  while  the  igneous  includes 
granite,  syenite,  porphyry,  etc. 
The  Laurentian  occurs  in  four  areas.  The  Raleigh  area  is  a  belt 
20  or  25  miles  wide,  running  northeast  from  this  place  to  the  State 
line,  and  consisting  of  light-colored  and  gray  gneisses  which  occa- 
sionally pass  into  granite.  These  are  cut  by  coarse  syenite  and  dio- 
rite  dikes.  The  second,  the  Salisbury  granite  area,  is  from  10  to  30 
miles  wide,  and  has  'an  area  of  about  3,000  square  miles.  The  preva- 
lent rocks  are  syenite,  dolerite,  greenstone,  amphibolite,  granite,  por- 
phyry, and  trachyte.  In  it  there  is  no  well-defined  gneiss,  mica 
slate,  serpentine,  or  limestone.  The  large  area  of  Mecklenburg  sye- 
nite is  regarded  as  the  oldest  rock  of  North  Carolina,  the  bottom  of 
the  Laurentian.  West  of  the  Salisbury  area  is  the  largest  connected 
area  of  Laurentian  in  the  State,  covering  not  less  than  16,000  square 
miles.  It  closely  resembles  the  Raleigh  area,  especially  in  the  south- 
eastern part,  where  it  consists  of  a  succession  of  schists,  gneisses,  and 
slates,  for  the  most  part  thin  bedded,  and  only  occasionally  showing 
granite-like  masses  and  syenites,  which  are  generally  in  the  forms  of 
dikes.  Belonging  with  this  series  are  probably  the  interstratified 
crystalline  limestones  of  Forsyth,  Yadkin,  and  Stokes.  The  outcrops 
are  generally  limited  to  2  or  3  rods  in  thickness,  a  few  hundred  yards 
in  length,  and  seem  to  graduate  into  the  neighboring  gneisses.  The 
fourth  considerable  area  of  Laurentian  rocks,  occupying  an  area  of 
3,000  or  4,000  square  miles,  is  west  of  the  Blue  Ridge,  between  this 
range  and  the  Smoky  Mountains.  This  is  probably  a  continuation  of 
the  preceding  belt,  being  separated  from  it  by  a  narrow  belt  of  Hu- 
ronian slates,  and,  like  it,  containing  crystalline  limestones. 
The  Huronian  follows  the  Laurentian  without  a  break  of  geological 
continuity.  These  rocks  are  found  in  five  principal  lines  of  out- 
crops, viz :  East  of  the  Raleigh  Lanrentian ;  between  the  Raleigh  and 
the  Salisbury  granite ;  west  of  the  Salisbury  granite,  the  Kings  Moun- 
tain belt;  the  Blue  Ridge  mountains;  and  the  Great  Smoky  Moun- 
tains, called  the  Cherokee  slates.  These  belts  are  placed  with  the 
Huronian  because  they  succeed  the  Laurentian  and  because  they  differ 
